The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The invention deals with a petroleum scope, particularly, techniques to stimulate formation production when oil recovering.
A severe problem in oil recovery is proppant carrying-over out of a fracture into a borehole upon hydraulic fracturing, both when primary cleaning and in some instances even upon well completion. In practice, up to 20% of proppant can be carried-over into a borehole, which poses serious threats, such as mentioned below. With low-yield wells, the proppant will be deposited in casings, which calls for intermittent flushing and results in repair procedure appreciation too. Another effect of carrying-over the unfixed proppant or grits should be early wear and breakdown of in-the-hole electric centrifugal pumps. The decrease should be observed in oil or gas recovery due to significant borehole area transmissibility because of fracture thickness reduction or production zone bridging.
Some techniques are known to markedly reduce the carrying-over proppant or other propping agents out of the fracture.
The most popular approach uses a solidified resin-coated proppant to be injected into the fracture at the end of treatment. However, this proppant is of limited application due to adverse chemical reaction of the resin coating and the hydraulic fracturing liquid. On the one hand, this interaction will cause partial coating degradation and integrity breaking, which reduces the proppant particle contacts and, therefore, the proppant packing strength. On the other hand, the reaction of the resin coating components and the hydraulic fracturing liquid components will lead to uncontrolled variation in the Theological liquid characteristics, which decreases hydraulic fracturing efficiency. Factors above and intermittent cyclic loads due to the borehole closing and development, and long period of the borehole closing could materially reduce the proppant packing strength.
A technique is known wherein to limit the formation-situated proppant carrying-over a fiber material mixed with the propping agent material should be added; thus, the fibers will interlock the proppant particles, which gives them higher strength and, therefore, limits back proppant carrying-over. Moreover, with fiber added, the loads will be shifted more effective and extra bridges will be across the significant proppant packing area. A fiber structure is more flexible as compared to the vulcanized resin proppant, therefore, movements will be admissible for a fiber-proppant packing without loss of strength.
A technique is known wherein the use of the bundles of fibers comprised about 5-200 individual fibers of 0.8-2.5 mm in length and approximately 10-1000 micrometers in diameter keeps from proppant carrying-over out of the borehole. With this, the structure of the fiber bundles is one-side fixed.
A technique is known of mixing proppant and strained material as bead-shaped particles. In doing so, the particles strained are made of polymer. The polymer particles strained can be of various shapes, such as oval, wedge, cubic, rodlike, cylindrical, and conic ones, however, the maximum length-to-base ratio being less or equal to 5. In case of strained materials of cone diameters and for aluminum particles, the maximum length-to-base ratio should be less or equal to 25. The particles strained can also be sphere-shaped plastic beads or composite particles containing undistorted cores and strained coatings. Usually, the volume of the undistorted core constitutes approximately 50-95% vol. of total particle and can be quartz, crystobalite, graphite, gypsum or talc. With another version (U.S. Pat. No. 6,330,916), a core consists of the materials strained and can comprise ground or sized materials, such as nutshell, seed shell, fruit kernels, and timber surfaced.
To fix and limit propping agent carrying-over the mixture of proppant and adhesive polymer materials can be used. Adhesive compounds will come into mechanical contact with propping agent particles, cover them and coat them with a thin adhered layer. As a result, particles will adhere with each other, as well as with sand or sized propping agent fragments; which stops to great extent or in full the grit carrying-over out of the fracture. A peculiar feature of the adhesive compounds is an adhesive property at higher subsurface temperatures for a long time without cross-linking or curing.
The adhesive materials can match other chemical agents used in hydraulic fracturing, such as, inhibitors, antimicrobial agents, polymer gel decomposers, and paraffin and corrosion inhibitors.
A technique is known of fracture propping using adhesive agents and resin proppants. U.S. Pat. No. 6,742,590 has disclosed a technique of fracture protection against carrying-over a proppant in the mixture of adhesive materials and strained particles being themselves effective additives to prevent the proppant carrying-over.
Another type of material used to prevent the proppant carrying-over is thermoplastic material. Thermoplastics mixed with a propping agent can soften at high rock temperatures and further adhere it formed a bonded aggregates with great of proppant amount.
A technique is known of using thermoplastics mixed with resin proppant. In some techniques, a thermoplastic material will mix with a proppant as liquid or solution in a suitable solvent. With this, an elastomer-forming compound can cure formed a thermoplastic material by itself or under special extra agents.
There remains a need to further prevent of the proppant carrying-over with improved production cost and manufacturing requirements. This need is met, at least in part, with the following invention.